The invention described here relates to novel naringenin derivatives and use thereof. More particularly, it relates to novel naringenin derivatives by which food pulse seeds such as azuki bean (Vigna angularis), cowpea (Vigna unguiculata), and mungbean (Vigna radiata) can effectively be protected from feeding by bean weevils and to insecticidal compositions comprising the novel naringenin derivatives as active components.
Control of crops from injurious insects is practiced to ensure stability of the yield and the quality of harvested products.
From the early 20th century, such synthetic insecticides as organic chlorides or organic phosphorus compounds, have been employed in controlling such injurious insects, and have greatly contributed to agricultural production.
In recent years, however, environmental protection or safety has resulted in a decline in use of synthetic insecticides.
As the amount of synthetic insecticides used increases, it has been reported that insects acquire chemical tolerance to these insecticides. Therefore, alternative new technologies are desired to replace synthetic insecticides.
In general, insecticides derived from naturally occurring products are considered to be less harmful to the environment.
In particular, a variety of natural compounds of plant origin have been used as insecticides, these include such compounds as pyrethroids. Flavonoid glycosides are a group of compounds produced by plants. The flavonoids are considered to contribute to antibacterial activity, enzyme inhibition, prevention from feeding injury by insects, and hormone action. Though all their functions in plants have yet to be elucidated.
The flavonoid, 6-C-xcex2-D-glucosyl-luteolin has an insecticidal effecton larva of giant tobacco budworm (Heliothis obsoleta Fabricius). There have been no reports of the effect of flavonoids on bean weevils.
Bean weevils are small beetles that are distributed in the tropical or subtropical zone. The bean weevils include azuki bean weevil (Callosobruchus chinensis) and cowpea weevil (Callosobruchus maculatus), and they feed on the seeds of azuki bean, rice bean (Vigna umbellata), cowpeas, and mung bean. Among them, cowpea weevil, which is distributed in Africa and Southeast Asia, are a major grain pest could spread outside the tropics if global warming continues.
Adult bean weevils fly into bean fields, where they lay eggs on young bean pods. The hatched larvae eat into the seeds, and later emerge from bean seeds after harvesting in seed storage areas. The emerged adult bean weevils lay eggs on the beans in storage faculties. Thus, as the generations of bean weevil are repeated, damage to seeds increases.
The life cycle of bean weevils can speed up when the environmental conditions are good, and thus cause great damage to beans in storage by feeding injury. Therefore, the protection of beans in the field from adult bean weevils has long been performed by scattering of agrochemicals or by treatment with chemicals after harvesting.
It is very difficult, however, to exterminate all the larvae of bean weevils invading bean seeds since the adults have high mobility. Extermination of the larvae which have invaded into the bean seeds is also difficult. To date, damage by bean weevils remains a serious problem despite control measures.
Therefore, there is a worldwide need for new and effective preventive methods.
The purpose of the invention described here is to provide novel naringenin derivatives of natural (plant) origin, having insect resistance, wherein it is possible to solve the above-mentioned problems and control bean weevils which cause feeding injury to grain legume seeds during ripening in the field and in storage. The purpose of the invention is also to provide insecticidal compositions comprising the novel naringenin derivatives as active components.
The present inventors worked assiduously to solve the above-mentioned problems and found that an edible bean native to Japan, i.e., rice bean (Vigna umbellata), exhibits a high level of insecticidal action (insect resistance) to be an weevils including azuki bean weevil and cowpea weevil. The rice bean was selected from 500 strains of leguminous seeds in the National Institute of Agrobiological Sciences, Japan, germplasm collections.
The seeds of rice bean contain an active component having an insecticidal action (insect resistance) to bean weevils. In addition, since the seeds of rice bean are edible, the active component contained therein is considered to be safe for humans in the concentrations they are present in rice bean.
In order to elucidate the factor(s) related to resistance in rice bean to bean weevils, the present inventors used various methods and extraction solvents to isolate an insecticidally active substance from the seed powder of rice bean. They found novel naringenin derivatives that have not yet been described in the literature. The invention was completed based on these findings.
According to the 1st aspect, the present invention provides a novel naringenin derivative of the general formula (I): 
(wherein R1 and R2 each represents either a hydrogen atom or xcex2-D-glucosyl group, but R1 and R2 cannot both have the same chemical structure).
Next, according to the 2nd aspect the invention provides an insecticidal composition comprising the naringenin derivative according to the 1st aspect as an active component.
Moreover, according to the 3rd aspect the invention provides an insecticidal composition according to the 2nd aspect, wherein the insecticidal composition is injurious to insects feeding on legume seeds.
Moreover, according to the 4th aspect the invention provides an insecticidal composition according to the 3rd aspect, wherein the injured legume seed eating insects are bean weevils.